The present invention relates to tire pressure monitoring systems, and in particular to implementing algorithms therefor. Still more particularly, the present invention relates to a tire pressure monitoring system algorithm for use with vehicles having dual placards for recommended rear tire pressures.
Recommended tire pressures are provided by motor vehicle manufacturers in the form of placards, usually located on the driver""s side door for ready reference by the driver. Motor vehicle tire pressures should be maintained by the driver at the placard tire pressure recommendations for safe vehicle operation and optimized ride and handling.
An interesting aspect in this regard are pick-up trucks and certain other motor vehicles, in that they are at various times operated with or without loads applied to the rear axle. These loads can be the result of cargo in the vehicle and/or trailering. These motor vehicles have a high rear placard tire pressure recommendation which is applicable when the vehicle is under a load condition. These motor vehicles further have a low rear placard tire pressure recommendation which is applicable when the vehicle is operated in an unloaded condition. This dual placard application presumes the driver would change the rear tire pressures to the proper placard recommendation depending on the load condition of the vehicle. By operating the vehicle at the proper tire pressure placard recommendation, ride, handling and over-all vehicle operation are optimized to suit the load condition of the vehicle. By way of example, the high placard tire pressure recommendation could be about 80 psi, and the low placard tire pressure recommendation could be about 53 psi.
The National Highway Traffic Safety Administration (NHTSA) now requires motor vehicle manufacturers to implement a tire pressure monitoring system to alert a driver to a low tire pressure condition. At present, the NHTSA requires the driver be alerted should the tire pressure drop below the greater of: 1) 75% of the placard tire pressure recommendation or 2) a minimum activation pressure defined in FMVSS 138 for the specific tires on the vehicle.
FIGS. 1 and 2 depict a motor vehicle 10 having a conventional tire pressure monitoring system 12 and an algorithm 50 for its implementation.
Referring firstly to FIG. 1, the tire pressure monitoring (TPM) system 12 includes an implementing microprocessor, electronics and software. The TPM system 12 is connected by a data links 14 to tire pressure sensors 16a, 16b, one for each tire of the vehicle (only the rear tires 18a, 18b being shown). Each tire pressure sensor 16a, 16b are pneumatically interfaced with its respective tire 18a, 18b and senses the pressure P1, P2 respectively therewithin. In the event the TPM system 12 determines a tire has a pressure that is not above a predetermined threshold, a signal device 22, as for example a warning light on the dashboard, is activated via a connection 24.
Referring now to FIG. 2, the software of the TPM system 12 implements the algorithm 50. At execution Block 52 the TPM system 12 is initialized automatically, for example when the ignition key is switched to the ON position. At execution Block 54, the algorithm acquires the tire pressure data from all the tire pressure sensors. At decision Block 56, the algorithm inquires whether the tire pressures are above the threshold appropriate for the placard pressure recommendation (for example that appropriate for compliance with FMVSS 138). If not, the algorithm causes the TPM system 12 to activate the warning signal 22 at execution Block 58. Otherwise, the algorithm returns to execution Block 54 and repeats the aforesaid steps with a predetermined periodicity.
Problematically, in vehicles having dual placard tire pressure recommendations the conventional TPM system 12 is not suited to provide a low tire pressure warning for the tires under dual placard. There are several reasons for this. One is that if the threshold in Block 56 is set for high placard pressure threshold, then when the driver changes the tire pressure to the low placard pressure, the warning signal will be activated. The other reason is that if the threshold is set for the low placard pressure threshold and the tires are inflated to the high placard pressure, then the TPM system 12 will not recognize a low pressure problem at the high placard pressure threshold.
Therefore, what remains needed in the art is a tire pressure monitoring algorithm which is operable in dual placard applications.
The present invention is a dual placard algorithm implemented in a tire pressure monitoring system which responds to tire inflation changes caused by the driver, and is thereby able to allow the tire pressure monitoring system to detect low tire pressure in dual placard applications.
Based upon tire pressure data acquisition by a TPM system, the dual placard algorithm according to the present invention automatically sets the threshold of the TPM system algorithm to that appropriate for the high placard pressure in the event the driver has inflated the rear tires to the high placard pressure recommendation. If the driver subsequently deflates the rear tire pressure to the low placard pressure recommendation, the dual placard algorithm alerts the driver, through the TPM system, that the pressure is low for the current high pressure placard and that the threshold for detecting a rear tire low tire pressure condition must be re-set. The driver then is required to take appropriate action. This action is to check the tires if the threshold is already set for that appropriate for the low placard pressure recommendation, or to cause the dual placard algorithm to enter a xe2x80x9clearn modexe2x80x9d in order to automatically re-set the threshold to that appropriate for the low placard pressure recommendation if the threshold is still set for that appropriate for the high placard pressure recommendation even though the rear tires were deflated to the low placard pressure recommendation. The dual placard algorithm can select the threshold appropriate for the low placard pressure recommendation only if the driver has deflated both rear tires to the low placard tire pressure recommendation.
It will be appreciated that the dual placard algorithm according to the present invention automatically maintains FMVSS 138 compliance in dual placard applications, eliminates need for a driver to select by a switch whether the vehicle is operating in a load or no load condition (that is, the threshold selection is appropriate for the high or low placard pressure recommendation), and further alerts the driver of an inappropriate threshold in the event the tire pressure has been changed from the high to the low placard pressure recommendation.
Accordingly, it is an object of the present invention to provide a dual placard algorithm implemented in a tire pressure monitoring system which responds to tire inflation changes caused by the driver, and is thereby able to allow the tire pressure monitoring system to detect low tire pressure in dual placard applications.
This and additional objects, features and advantages of the present invention will become clearer from the following specification of a preferred embodiment.